This invention relates to a grab bucket and more particularly to a grab bucket especially suitable for dredging sludge accumulated on the bottom of the sea, rivers, lakes, etc.
Hitherto it has been wellknown that when the sludge accumulated on the bottom of the sea, rivers, lakes or the like is dredged by a conventional grab bucket comprising a pair of bucket shells, during the winding up movement of the bucket from the bottom of the sea, etc. to the surface, the sludge exposed over the upper openings of the shells constituting the grab bucket is washed down by the surrounding water moving relative to the bucket so that the water around the dredging area is vastly polluted. On the other hand, on dredging the bottom of the sea, etc., should the grab bucket drive too deeply into the soft mud on the bottom so that it is apt to take up too much sludge, pollution of the water may also be caused near the bottom due to the unnecessary agitation of the sludge accumulated on the bottom.